Abstract

A 360-degree rotating jetting tool has been successfully deployed to cleanup about 1000 ft of 6.25" horizontal open-hole gravel packed (OHGP) well. The exercise was carried out using Nitrified 10% HCl placed from the toe to the heel at Coil Tubing average rate of 20 ft/min. Three passes were made at total fluids rate of 1.0 bpm. During the fluid placement, no losses were encountered. After the treatment and initial production testing, a baseline memory production log (MPLT) was acquired across the horizontal drain section to evaluate the completion/cleanup efficiency. The MPLT results indicated a better drain hole cleanup as seen in the inflow profile of the completed drain section. Higher contribution was also noticeable in the cleaner sand members. From the result obtained, the 360-degree rotating jetting tool can be efficiently applied to cleanup drain holes especially in horizontal wells equipped with gravel packs.

Introduction

This paper discusses the maiden application of a 360-degree rotating jetting tool (as shown in figure 1) in the clean-up of a gravel packed horizontal well, evaluates the inflow profile (based on memory production log) as a yardstick for determining the tool's efficiency, and demonstrates the economic impact on the bottom-line business as seen in Well OBGN-XA located in Obigbo-North field of Niger Delta, Nigeria as indicated in figure 2.

In the past, most wells completed in the field and on the D2.300A reservoir were conventional with poor inflow and/or productivity index. The problem of water conning associated with high drawdown, sand production and by-passed oil were common. Thus, to achieve the primary objective earlier defined against Well OBGN-XA, the initial well plan was to drill and complete the Well OBGN-XA as a horizontal well, so as to improve the inflow area, lateral connectivity of by-passed oil and install gravel pack to combat anticipated sand failure. However, ensuring an effective cleanup of the horizontal drain section to enhance actual well productivity was a critical challenge.

Proper treatment fluid placement and complete coverage during displacement were often hampered by high permeability streaks which could act as localized "thief zones". Before now, the traditional practice of cleaning up newly completed horizontal wells was to spot the treatment acid with coil tubing across the entire drain-length; usually, the acid is foamed to achieve a better diversion and placement. However, post cleanup production logs taken across the horizontal drain section do not confirm a fully satisfactory cleanup, as some sections of the drain-hole do not effectively contribute to inflow into the liner-bore. The situation poses a greater challenge in horizontally gravel packed wells as getting the treatment fluid to reach and dissolve the filter-cake will require energy sufficient to overcome the fluid attenuation effect due to the gravel and the screen. The high velocity 360-degree jetting tool concept easily provides the needed energy.

The initial considerations to achieve a better cleanup of Well OBGN-XA (in figure 3) were the wash-cup approach, acid spotting using coil tubing and a trial application of the newly commercialized 360° high velocity jetting tool oriented nozzles). The jetting tool was considered for a trial based on its technical feasibility, logistics, cost and potential to address the main challenge of getting the treatment fluid to the filter-cake. The tool's efficiency was to be primarily evaluated using memory production logs acquired across the drain-hole.

Well Descriptions

Well OBGN-XA located in Obigbo-North field is the first horizontal open-hole gravel packed well in SPDC. It is also on record as the first successful one in the Niger Delta. The well was completed in the D2.300A reservoir.

The primary objective of Well OBGN-XA was to develop about 8.5 MMstb of oil at an off-take rate of 3000 bopd on the D2.300A reservoir as detailed in table-1. The D2.300A reservoir in Obigbo-North field has a total expectation STOIIP of about 50.0 MMstb and a UR of 24.9 MMstb. This represents some 49.0 % recovery factor.

Structurally, the D2.300A reservoir is a rollover anticline associated with large East-West trending growth faults. The reservoir is successive distributary channels. The entire D2.300A reservoir is subdivided by thin permeable radioactive sand into two separate layers. The reservoir is well developed and laterally extensive with an average thickness of 60-ft.

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